A wave soldering tank typically includes a pump submerged within molten solder in the tank. When the pump is operated, molten solder is sucked into an inlet of the pump and then discharged from a nozzle communicating with an outlet of the pump. By suitably controlling the pump, the solder discharged from the nozzle can be formed into a wave through which electronic parts can be passed for soldering.
FIG. 1 is a schematic plan view of a conventional wave soldering tank disclosed in Japanese Published Unexamined Patent Application 2003-136233. As shown in this figure, a solder feed chamber 94 which is disposed in a soldering tank 90 includes a casing 92 in which a multiple-blade centrifugal pump 91 (such as a sirocco pump) is provided. The solder feed chamber 94 communicates with a nozzle 93 from which molten solder can be discharged.
With this conventional apparatus, only approximately ¼ of the entire periphery of the casing 92 is open for molten solder to be discharged therefrom to the solder feed chamber 94. At point A in FIG. 1, the molten solder discharged from the pump 91 is traveling approximately tangentially with respect to the pump 91. Point B is spaced from point A by approximately ¼ of the distance around the pump 91. There is a big difference in the discharge speed of molten solder between the vicinity of point A and the vicinity of point B, and this speed difference may produce undesirable undulations in solder which is discharged from the nozzle 93. In order to minimize the undulations, flow straightening plates (not shown) are commonly provided in a duct 94 leading from the casing 92.